1. Field of the Invention
The present invention relates to a head suspension in a hard disk drive incorporated in an information processing apparatus such as a computer. In particular, the present invention relates to a head suspension with a multilayer ground, a method of manufacturing the same, a flexure with a multilayer ground, and a method of manufacturing the same.
2. Description of Related Art
A head suspension used for a hard disk drive (HDD) has a flexure. According to a related art, the flexure has a four-layer structure including a substrate made of a resilient stainless steel thin plate, a base insulating layer made of flexible resin and covering the substrate, write (record) and read (reproduce) signal wiring formed on the base insulating layer and connected to a magnetic head, and a cover insulating layer made of flexible resin and covering the wiring.
According to the related art, write and read signals transmitted through the head suspension use the stainless-steel substrate of the flexure as an electrical ground. The stainless-steel substrate has a low conductivity, which is about 1/50 of that of copper. Due to this, the stainless-steel substrate causes a large signal transmission loss (hereinafter referred to simply as “loss” or “transmission loss”) and a narrow frequency band.
To cope with this, there is a known technique to arrange a copper ground layer between the stainless-steel substrate and the base insulating layer, to lower a wiring impedance, decrease the loss, and widen the frequency band.
The wiring impedance must be low on the write (record) side to minimize the loss and widen the frequency band. On the other hand, the wiring impedance must be high on the read (reproduce) side to increase an input impedance at a preamplifier, to expand a voltage signal to the preamplifier.
If the copper ground layer is arranged to entirely cover the width of the stainless-steel substrate, the wiring impedance on the read side is decreased. Namely, the related art is unable to lower wiring impedance on the write side, and at the same time, increase wiring impedance on the read side.
The above-mentioned related art is disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2003-249046.